Abstract
This work focuses on the simulation and experimental study of directional wicking of water on a surface structured by open microchannels. Stainless steel was chosen as the material for the structure motivated by industrial applications as fuel cells. Inspired by nature and literature, we designed a fin type structure. Using Selective Laser Melting (SLM) the fin type structure was manufactured additively with a resolution down to about 30 μm. The geometry was manufactured with three different scalings and both the experiments and the simulation show that the efficiency of the water transport depends on dimensionless numbers such as Reynolds and Capillary numbers. Full 3D numerical simulations of the multiphase Navier-Stokes equations using Volume of Fluid (VOF) and Lattice-Boltzmann (LBM) methods reproduce qualitatively the experimental results and provide new insight into the details of dynamics at small space and time scales. The influence of the static contact angle on the directional wicking was also studied. The simulation enabled estimation of the contact angle threshold beyond which transport vanishes in addition to the optimal contact angle for transport.
Highlights
In microfluidics, water forms droplets which remain pinned on solid surfaces
Weber number (We) argue that the chemical and topographic defects of the melted metal surfaces visible in the first panel are responsible for this pinning effect
The smaller resolution of the numerical approach uncovers the details of these different phases which we describe in the case of a 50◦ contact angle
Summary
Water forms droplets which remain pinned on solid surfaces. Liquid motion is provided by a pump or an external energy input such as piezo elements. Surface heterogeneity as a gradient of wettability, i.e., the solid-liquid contact angle, allows droplet spreading without any external energy input [1,2]. It is a relaxation dynamics of the drop/surface system which decreases its free energy. Such liquid movement is usually called passive transport when the liquid flow has a privileged direction. Passive water transport at microscale offers many applications [3,4]
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